In modern airports the terminal is located relatively far from the runaways. Airplanes use their jet engines to travel from the terminal to a runaway (said operation is also known as taxi-out) and to travel from a runway to the terminal (said operation is also known as taxi-in).
These jet engines are very noisy, cause safety hazards, burn large quantities of fuel and cause to significant air pollution, the emission of large quantities of CO2.
Taxi traffic delay is the largest of all aviation movements delay, the average taxi-out delay in minutes per flight is approximately twice the airborne delay. Although aircraft burn roughly 5 times faster when airborne, crew and equipment costs make the spend rate for taxiing aircraft about ⅔ that for airborne aircraft. Consequently, the cost of taxi-out delay exceeds that of airborne delay by about ⅓, totaling more than 1 B$ annually. By automated tower controlled ground movement, one shall save significantly on taxi delays, which make significant annual cost. This shall add to the savings from fuel burned during taxi performed by towing tractors or robots.
Jet fuel is one of the two largest airlines operating expenses (the other being labor cost), constituting 25-30% of typical airline annual operation cost. Therefore, saving in fuel consumption is one of the major efforts for all airlines today. Jet fuel prices increased from less than 1$/gal in 2001 to 2$/gal in 2006 and is expected to reach 2.5 $/gal or higher by 2010, making the issue critical for the airline industry.
During taxi, typical aircraft fuel consumption is about 3200 lbs per hour (9.0 gallon per minute). Typical taxi-out time today is 30 minutes and rising constantly with the increase of air traffic all over the world. On average, typically, taxi-out time is 3 times longer than taxi-in time. Thus, a minimum of 40 minutes of taxi-out plus taxi-in time burn 360 gallons of fuel on airport grounds per flight, and this number is growing.
Air pollution in airports evolved into a major and significant hazard, and it keeps evolving due to the increment in air traffic worldwide. Gas emission in a jet engine is around 8 Kg of CO2 per gallon. In a typical 40 minutes taxi-out plus taxi-in time, an aircraft emits 2.9 ton of CO2, a very critical issue.
By 2010, the forecast is of more than one billion (1 B) air travels, or around fifteen million (15 M) flights a year, only in the US, not relating to the worldwide air traffic. For every 100 gallon of fuel saved during taxiing per flight, it is about 3.0 B$ in fuel and 12 M ton in CO2 emission, in the US.
A typical busy airport has more than 1000 departures a day or around 400,000 flights a year. Every 100 gallon of fuel saved per flight, transfers in 40 M gallon fuel saved per year per airport, or 80 M$ yearly savings in fuel expenditure per airport (2$/gal today), actual savings being much higher.
In order to reduce the usage of jet engines various airplane towing systems were provided. Some are illustrated in the following patents and patent applications, all being incorporated herein by reference: U.S. Pat. No. 6,305,484 of Leblanc; U.S. Pat. No. 5,219,033 of Pollner et al.; U.S. Pat. No. 5,314,287 of Wichert; U.S. Pat. No. 5,860,785 of Eberspacher; U.S. Pat. No. 6,283,696 of Trummer et al.; U.S. Pat. No. 6,352,130 of Klein et al.; U.S. Pat. No. 6,543,790 of Johnson; U.S. Pat. No. 6,675,920 of Diez et al.; U.S. Patent application publication serial No. 2006/0056949 of Eckert; U.S. Patent application publication serial No. 2003/095854 of Abela; U.S. Patent application publication serial No. 2005/196256 of Rodenkirch et al.; European patent application 649787A1 of Michelson et al and PCT patent application publication serial number WO/04028903A1 of Maggiori.
There is a need to provide an efficient method and system for transferring an airplane.